Underestimated Ammonia Emissions from Road Vehicles

Abstract

In this study, we use comprehensive vehicle emission remote sensing measurements of over 230,000 passenger cars to estimate total UK ammonia (NH₃) emissions. Estimates are made using "top-down" and "bottom-up" methods that demonstrate good agreement to within 1.1% for total fuel consumed or CO₂ emitted. A central component of this study is the comprehensive nature of the bottom-up emission estimates that combine highly detailed remote sensing emission data with over 4000 km of 1 Hz real driving data. Total annual UK NH₃ emissions from gasoline passenger cars are estimated to be 7.8 ± 0.3 kt from the bottom-up estimate compared with 3.0 ± 1.7 kt reported by the UK national inventory. An important conclusion from the analysis is that both methodologies confirm that gasoline passenger car NH₃ emissions are underestimated by a factor of about 2.6 compared with the 2018 UK National Atmospheric Emissions Inventory. Furthermore, we find that inventory estimates of urban emissions of NH₃ for passenger cars are underestimated by a factor of 17.